Apparatus and method for determining mounting state of a trailer tracking device

ABSTRACT

A cargo tracking apparatus for detecting proximity to a cargo structure includes a cargo sensor, a location sensor, a wireless transmitter, and a processor, all disposed within a housing that is configured to be attached to the cargo structure. The cargo sensor, which is adjacent a sensor window in the housing, detects a portion of the cargo structure disposed near the sensor window and generates a cargo sensor signal based on detection or lack of detection of the cargo structure. The location sensor generates location information based on the location of the cargo tracking apparatus. The processor receives the cargo sensor signal and the location information, and based thereon generates alert messages that contain the location information and information indicative of whether the cargo structure is disposed near the cargo tracking apparatus. The wireless transmitter transmits the alert messages.

RELATED APPLICATIONS

This application claims priority to provisional patent application Ser.No. 62/640,283, filed Mar. 8, 2018, titled Apparatus and Method forDetermining Mounting State of a Trailer Tracking Device.

FIELD

This invention relates to the field of mobile asset tracking andmanagement. More particularly, this invention relates to a system fordetermining whether a cargo container tracking device is in closeproximity to a cargo container.

BACKGROUND

Fleet management and cargo shipping companies use tracking devicesinstalled on cargo containers to keep track of the location of thecontainers. Such devices typically use GPS receivers to determinelocation coordinates and wireless data transceivers to transmit locationinformation and alert messages via wireless networks to central cargomanagement servers. The cargo containers may be twenty foot long orforty foot long foot shipping containers well known in the art or theymay be cargo trailers of about the same dimensions that are pulled bytractors.

In most cases, the tracking devices are self-contained units that aremounted to an outside surface of a container or trailer. There is a needfor cargo management personnel to know when a cargo tracking device isremoved from a trailer or other cargo container. There is also a need toknow whether or not a cargo container has been loaded onto a trailer.

Current solutions are indirect, expensive, hard to install, have limitedsense distances, lead to false alerts, and can result in alerts that arenot received when something happens.

What is needed, therefore, is a cargo tracking device that overcomes thedeficiencies of the prior art.

SUMMARY

The above and other needs are met by a cargo tracking apparatus fordetecting proximity to a cargo structure. In some embodiments, the cargotracking apparatus includes a housing, and a cargo sensor, a locationsensor, a wireless transmitter, and a processor that are disposed withinthe housing. The housing, which is configured to be attached to thecargo structure, has a sensor window. The cargo sensor, which isadjacent the sensor window, detects a portion of the cargo structuredisposed adjacent the sensor window and generates a cargo sensor signalbased on detection or lack of detection of the portion of the cargostructure. The location sensor generates location information based onthe location of the cargo tracking apparatus. The processor receives thecargo sensor signal and the location information, and based thereongenerates alert messages. The alert messages contain the locationinformation and information indicative of whether the cargo structure isdisposed in proximity to the cargo tracking apparatus. The wirelesstransmitter transmits the alert messages.

In some embodiments, the cargo sensor comprises a Time of Flight (ToF)sensor, an optical sensor, a reed switch, a Radio Frequency (RF) sensor,or a capacitive sensor.

In some embodiments, the sensor window is transparent at infraredwavelengths, and the cargo sensor is a ToF sensor that periodicallymakes a distance measurement through the sensor window, wherein thecargo sensor signal includes information indicative of the distancemeasurement. The processor generates an alert message if the distancemeasurement is greater than a predetermined amount, thereby indicatingthat the cargo tracking apparatus is not in proximity to the cargostructure.

In some embodiments, the sensor window is transparent at opticalwavelengths, and the cargo sensor is an optical sensor that detects thepresence of the portion of the cargo structure adjacent the sensorwindow. The processor generates an alert message if no portion of thecargo structure is detected adjacent the sensor window, therebyindicating that the cargo tracking apparatus is not in proximity to thecargo structure.

In some embodiments, the cargo structure includes a metallic portion,the sensor window is transparent to Radio Frequency (RF) signals, andthe cargo sensor is an RF sensor that is operable to detect the presenceof the metallic portion adjacent the sensor window. The processorgenerates an alert message if the metallic portion is not detected,thereby indicating that the cargo tracking apparatus is not in proximityto the cargo structure.

In some embodiments, the cargo structure includes a metallic portion,the sensor window in the housing is transparent to electric fields, andthe cargo sensor is a capacitive sensor that is operable to detect thepresence of the metallic portion of the cargo structure adjacent thesensor window. The processor generates an alert message if the metallicportion is not detected, thereby indicating that the cargo trackingapparatus is not in proximity to the cargo structure.

In some embodiments, the location sensor comprises a GPS receiver.

In some embodiments, the wireless transceiver comprises a cellular datatransceiver or a Wi-Fi transceiver.

In another aspect, embodiments described herein are directed to anapparatus for detecting whether a cargo tracking device is attached to acargo structure. The apparatus includes one or more first short-rangeradio frequency transceivers attached to the cargo structure. The cargotracking device, which is configured to be attached to the cargostructure includes a location sensor, a second short-range radiotransceiver, a processor, and a wireless transmitter. The locationsensor generates location information based on the location of the cargotracking device. The second short-range radio frequency transceivercommunicates with the one or more first short-range radio frequencytransceivers via one or more communication links when the secondshort-range radio frequency transceiver is within communication range ofthe one or more first short-range radio frequency transceivers. Thesecond short-range radio frequency transceiver generates communicationlink status information indicating the status of the one or morecommunication links. The processor receives the location information andthe communication link status information, and based thereon generatesan alert message containing the location information and informationindicative of whether the cargo structure is disposed in proximity tothe cargo tracking device. The wireless transmitter transmits the alertmessage.

In some embodiments, the one or more first short-range radio frequencytransceivers are components of one or more sensor devices attached tothe cargo container for monitoring one or more physical characteristicsof the cargo structure.

In some embodiments, at least one of the one or more first short-rangeradio frequency transceivers is a component of a proximity buttonattached to the cargo structure.

In some embodiments, the processor generates the alert message only whenthe communication link status information indicates that all of the oneor more communication links have been interrupted.

In some embodiments, the first and second short-range radio frequencytransceivers comprise Bluetooth transceivers.

In some embodiments, the wireless transceiver comprises a cellular datatransceiver or a Wi-Fi transceiver.

In yet another aspect, embodiments described herein are directed to anapparatus for detecting proximity of a cargo container to a trailer. Theapparatus includes a container sensing device and a cargo trackingdevice. The container sensing device includes a first housing, and acargo sensor and a first short-range radio frequency transceiver thatare disposed within the first housing. The first housing, which isconfigured to be attached to the trailer, has a sensor window. The cargosensor, which is adjacent the sensor window, detects a portion of thecargo container that is adjacent the sensor window and generates cargosensor information based on detection or lack of detection of theportion of the cargo container. The first short-range radio frequencytransceiver transmits the cargo sensor information via a wirelesscommunication network. The cargo tracking device includes a secondhousing, and a second short-range radio frequency transceiver, aprocessor, and a wireless transmitter disposed within the secondhousing. The second short-range radio frequency transceiver receives thecargo sensor information via the wireless communication network. Theprocessor receives the cargo sensor information and based thereongenerates an alert message containing information indicative of whetherthe cargo container is disposed in proximity to the trailer. Thewireless transmitter transmits the alert message.

In some embodiments, the cargo tracking device includes a locationsensor for generating location information based on the location of thecargo tracking device. The processor of these embodiments generates thealert message including the location information.

In some embodiments, the cargo sensor comprises a ToF sensor, an opticalsensor, a Radio Frequency (RF) sensor, or a capacitive sensor.

In some embodiments, the first and second short-range radio frequencytransceivers comprise Bluetooth transceivers.

In some embodiments, the wireless transceiver comprises a cellular datatransceiver or a Wi-Fi transceiver.

In yet another aspect, embodiments described herein are directed to acargo detection apparatus for detecting the presence or absence of acargo container on a cargo trailer, wherein the cargo trailer has achassis and one or more suspension springs. The cargo detectionapparatus includes a housing configured to be attached to the chassis ofthe cargo trailer in proximity to at least one of the one or moresuspension springs. Within the housing is an inductive coil, aprocessor, and a wireless transmitter. The inductive coil generates aninductive coil voltage having a level that is related to the distancebetween the inductive coil and the suspension spring. The processorexecutes instructions that determine a relative change in distancebetween the inductive coil and the suspension spring based at least inpart on a change in the inductive coil voltage. The wireless transmittertransmits information indicative of the presence or absence of the cargocontainer on the cargo trailer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other embodiments of the invention will become apparent by reference tothe detailed description in conjunction with the figures, whereinelements are not to scale so as to more clearly show the details,wherein like reference numbers indicate like elements throughout theseveral views, and wherein:

FIGS. 1A-1C depict cargo proximity detection and tracking systemsaccording to embodiments described herein;

FIG. 2 depicts a cargo proximity detection and tracking apparatusaccording to a preferred embodiment;

FIGS. 3A and 3B depict a cargo tracking device incorporating a reedswitch and a magnet according to a first embodiment;

FIGS. 4A and 4B depict a cargo tracking device incorporating a reedswitch and a magnet according to a second embodiment;

FIG. 5 depicts a cargo proximity detection and tracking apparatusaccording to an alternative embodiment; and

FIGS. 6 and 7 depict a cargo proximity detection apparatus according toan alternative embodiment.

DETAILED DESCRIPTION

Embodiments of a tracking system described herein determine whether acargo tracking device is installed on or in close proximity to a cargostructure. As the term is used herein, a “cargo structure” refers to acargo trailer or cargo container or any other movable structure forholding and transporting cargo. Preferred methods include proximitytesting and system proximity detection.

As shown in FIGS. 1A-1C, a cargo tracking device 10 may be installed ona cargo container or on a cargo trailer that is pulled by a tractor. Inthe embodiment of FIGS. 1A and 1C, the tracking device 10 preferablystays attached to the cargo trailer when the trailer is switched fromone tractor to another. In the embodiment of FIG. 1B, the trackingdevice 10 may be installed on a cargo container that is transported on aflatbed trailer. This embodiment also includes a container sensor device42 that detects the presence of the cargo container on the trailer. Allof these embodiments implement one or more proximity sensingtechnologies as described hereinafter.

FIG. 2 depicts a preferred embodiment of the cargo tracking device 10.The device 10 includes a cargo sensor 14, location sensor 18, processor20, long-range wireless data transceiver 22, and short-range wirelessdata transceiver 44, all disposed within a housing 12. As described inmore detail hereinafter, the cargo sensor 14 may be a Time of Flight(TOF) sensor, an optical sensor, a reed switch, an RF sensor, or acapacitive sensor. In some embodiments, the cargo sensor 14 mayimplement more than one of the above listed sensor technologies. Withina wall of the housing 12 is a sensor window 16 through which the cargosensor 14 senses the presence or absence of a cargo structure 24. Forexample, the cargo structure 24 may be a wall or other surface of acargo container. In some embodiments, the window 16 is the entire wallof the housing, or the entire housing, if the housing is transparent tothe radiation of the sensor.

In a preferred embodiment, the location sensor 18 is a GlobalPositioning System (GPS) receiver that generates position coordinatesbased on timing signals received from GPS satellites. The long-rangewireless data transceiver 22 is operable to transmit and receive dataover wide area wireless data networks using one or more communicationprotocols, such as General Packet Radio Service (GPRS) or Long TermEvolution (LTE) wireless broadband technology. The short-range wirelessdata transceiver 44 is operable to transmit and receive data over localwireless data networks using one or more short-range communicationprotocols, such as Bluetooth, ZigBee, Z-Wave, WiFi, Thread, or WeMo. Theprocessor 20 executes software instructions for processing informationfrom the cargo sensor 14 and the location sensor 18, and generatingalert messages based on the cargo sensor information and locationinformation.

Proximity Testing

Time of Flight (ToF) Sensor

In some embodiments, the cargo sensor 14 comprises a Time of Flight(ToF) sensor, which is generally a laser-ranging camera system thatresolves distance based on the known speed of light. Thus, a ToF sensorperiodically measures the time-of-flight of a light signal between thesensor and a nearby object, such as the surface of the cargo structure24. If the measured distance (“d” in FIG. 2) is greater than apredetermined very small distance, then it is assumed that the trackingdevice has been removed from the cargo container, in which case an alertmessage is generated. In a ToF sensor embodiment, the sensor window 16is a portion of a wall of the housing 12 that is transparent to thewavelength of infrared light generated by the sensor. A very inexpensiveToF sensor may be used in this application is the ST Micro VL53L0X.Other Time of Flight technologies may be used here, such as ultrasonicsensors well known in the art.

Optical Sensor

In some embodiments, the cargo sensor 14 comprises an optical sensorthat detects the presence of a surface close to the tracking device 10using an optical proximity detector. An example is the Silicon Labsmodel Li1102. In the optical sensor embodiment, the sensor window 16 isa portion of a wall of the housing 12 that is transparent to thewavelength of visible light generated by the optical sensor.

Reed Switch

In some embodiments, the cargo sensor 14 comprises a reed switch, whichis an electrical switch operated by an applied magnetic field.Generally, a reed switch includes a pair of contacts attached toferromagnetic metal reeds within a hermetically sealed glass envelope.In some embodiments, the contacts are normally open, and they close whena magnetic field is applied. In other embodiments, the contacts arenormally closed, and they open when a magnetic field is applied. Ineither case, the switch is actuated by bringing a magnet in closeproximity to the switch. Once the magnet and the switch are separated,the switch goes back to its original position. Thus, in the reed switchembodiment of the cargo sensor 14, the sensor window 16 is a portion ofa wall of the housing 12 that is transparent to a magnetic field.

As depicted in FIGS. 3A and 3B, one embodiment includes a reed switch 28disposed within the housing 12 of the tracking device 10, and acorresponding disk-shaped magnet 30 disposed on the cargo structurewhere the tracking device 10 is to be attached. To address the challengeof how to install the magnet 30 on the cargo structure, the magnet 30 isinitially removably attached to an interior cover of the tracking device10, such as using a weak adhesive. On an outer surface of the housing 12is a strong adhesive surface, such as 3M™ VHB™ tape. When installing thetracking device 10 to a cargo structure, the installer removes aprotective cover from the strong adhesive tape and presses the exposedtape on the housing 12 against the cargo structure. During installation,the magnet 30 attaches to the mounting surface, and the weak adhesivebreaks off. Using a “twist-on” method to attach the tracking device 10,a magnet-width groove with a radius that is co-centered with the radiusof the mounting holder slides around the magnet that is secured to themounting surface. While the installer twists the housing 12 of thetracking unit 10 to install it, the magnet 30 rides in the groove 32until the tracker is seated. When the tracking device 10 is in itsseated position, the internal reed switch 28 is in position above themagnet 30, which causes the reed switch 28 to be activated. If thetracking device becomes unseated, the reed switch 28 is deactivated,which results in an indication to the tracking device that the trackingdevice has become unseated.

In an alternative embodiment, the magnet 30 may be held temporarily inplace using plastic features in the housing 12 of the tracking device10, rather than by a weak adhesive. As shown in FIGS. 4A and 4B, thehousing 12 of this embodiment includes a carrying channel 34 and a snapfeature 36 that holds the magnet 30 in place. Similar to what isdescribed above, the installer removes a protective film from a strongadhesive backing, and when the tracking device 10 is installed on thecargo structure, the adhesive bonds the magnet 30 to the cargostructure. As the installer twists the tracking device 10, the snapfeature 36 releases the magnet 30 from its original position and itremains fixed to the trailer while the tracking device 10 is rotated.

Radio Frequency (RF) Sensor

In some embodiments, the cargo sensor 14 comprises an RF sensor thatincludes an antenna, an RF transmitter, and an RF receiver. In theseembodiments, the sensor window 16 is a portion of a wall of the housing12 that is transparent to RF energy generated by the RF sensor, and thesurface of the cargo structure that is disposed in close proximity tothe RF sensor is metallic. The RF sensor periodically transmits a pulseor a string of pulses through the sensor window 16. If a metallicstructure is present on the opposite side of the window 16, the pulse orstring of pulses is reflected and the returned pulse or pulse string isaltered by being reflected. By analysis of the return signal, the RFreceiver determines whether the RF sensor's antenna is close to ametallic surface. In an alternative embodiment, the impedance of theantenna is continuously or periodically measured by an analog circuit.The proximity of a metallic surface alters the impedance of the antenna.When the impedance or other electrical characteristic of the antennachanges by a threshold amount, this indicates that the antenna has beenseparated from the metallic plane, and an alert message is generated.

Capacitive Sensor

In some embodiments, the cargo sensor 14 comprises a capacitive sensor.Such sensors are used in smartphones to detect the presence of a fingerin close proximity to a display screen. Using a large sense wire,capacitive sensor technology can be used to detect the presence of alarge metal body in proximity to the sensor 14. In these embodiments,the sensor window 16 is a portion of a wall of the housing 12 that istransparent to electromagnetic energy generated by the capacitivesensor. In an exemplary embodiment, the capacitive sensor includes along sense wire to implement CapSense capacitive touch sensingtechnology offered by Cypress Semiconductor Corp. With this technology,the sensing distance is directly proportional to the length of the sensewire. For example, a 15 cm sensing distance may be implemented using asense wire that is 15 cm in length.

System Proximity

System proximity embodiments rely on connectivity with certain othersystem components. If the connectivity is broken, then it is determinedthat the tracking device has been removed. These embodiments have adistinct advantage in that the connectivity function can be combinedwith other system functions, thereby reducing overall system cost, orproviding additional functionality at the same cost. In preferredembodiments, the system proximity embodiment may take any one of theforms described herein.

Dedicated Proximity Button

FIG. 1C depicts an exemplary embodiment that includes a proximity button38 mounted on a cargo trailer in a different location from that of thetracking device 10. The proximity button 38 includes a short-range RFtransceiver, such as a Bluetooth low-energy (LE) transceiver. Theshort-range RF transceiver in the button 38 is paired with a short-rangeRF transceiver in the tracking device 10, which may also be a BluetoothLE transceiver. If the short-range RF transceiver of the tracking device10 loses pairing with the short-range RF transceiver of the proximitybutton 38, this indicates that the tracking device 10 has been separatedfrom the trailer. Upon this indication, the tracking device 10 transmitsan alert message indicating that the connection has been lost, andappropriate action can be taken. The button 38 may be powered by aprimary cell, or a secondary cell which is recharged by a primary cell,a solar panel, vibration energy harvesting, or other environmentalharvesting methods.

The Proximity Button may also include its own long-range transceiver andlocation sensor, which is/are only activated when it is no longerconnected with the tracking device 10. Thus if the tracking device 10 isdestroyed, the Proximity Button may independently report the location ofthe cargo container.

It will be appreciated that the RF connection technology is not limitedto Bluetooth LE, but may be any RF connectivity protocol familiar to aperson having ordinary skill in the art. These RF connectivity protocolsmay also include ZigBee, Z-Wave, WiFi, Thread, WeMo or any otherstandard or proprietary wireless protocol. These RF connectivity methodsmay use industrial, scientific, and medical (ISM) bands such as the 433Mhz, 900 MHz, 2.4 GHz, 61 GHz, or any other ISM band. They may also usea licensed band if available.

Integrated System Functions

As depicted in FIG. 1C, in addition to or instead of the proximitybutton 38, the proximity function may be implemented using a trailerdoor sensor 40. Generally, the door sensor 40 is necessarily located atthe back of the trailer near the door, whereas the tracking device 10 isusually mounted on the front of the trailer near the attachment to thetractor. The door sensor 40 is preferably powered by a primary powercell, or a secondary cell system that is charged through a mechanismthat generates power through the motion of the trailer, such as avibration energy harvester. The door sensor 40 preferably includes an RFtransceiver, such as a Bluetooth LE transceiver, that maintains an RFconnection through a wireless interface with the tracking device 10. Thedoor sensor 40 may sense the open/closed the state of the trailer doorusing proximity sensing methods similar to those discussed herein.Although the RF wireless interface could be Bluetooth LE, a preferredembodiment uses a standard transceiver in the 900 MHz range to providebetter connectivity. Several protocols could be used in variousembodiments, such as ZigBee, Z-Wave, Thread, and WeMo, or a proprietaryinterface.

In the embodiment of FIG. 1C, the door sensor 40 not only provides thestatus of the door, but it also provides a presence indication, similarto the dedicated proximity button 38 discussed above. This presenceindication function could also be built into other sensors on thetrailer, such as weight sensors, tire pressure sensors, temperaturesensors, or any other sensor. A preferred embodiment may also improvereliability by looking for the presence of multiple paired sensors, anddetermining that the tracking device 10 has been removed based on theabsence of signals from all of the paired sensors. This limits thepossibility of false positives that could be triggered if there is cargoin the trailer that generates RF interference, thereby causing one ormore, but not all, of the sensors to lose connection to the trackingdevice 10.

Cargo Container Detection on Flatbed Trailer

FIGS. 1B and 5 depict a first embodiment for detecting and reportingwhether a cargo container is present on a flatbed trailer. Using thisfirst embodiment, the operator of the fleet of trailers can determineremotely when a container is separated from or dropped onto the trailer.This embodiment includes a container sensing device 42 mounted on theflatbed trailer. The container sensing device 42 includes a cargo sensor46 and a short-range wireless data transceiver 48 disposed within ahousing 50. The cargo sensor 46 preferably implements one or more of theabove listed sensor technologies. Within one or more of the walls of thehousing 50 is a sensor window 52 through which the cargo sensor 46senses the presence or absence of a cargo container 24.

The embodiment of FIGS. 1B and 5 also may include a tracking device 10attached to the cargo container. The tracking device 10 may include alocation sensor 18, processor 20, long-range wireless data transceiver22, and short-range wireless data transceiver 44, all disposed within ahousing 12. Preferably, the container sensing device 42 is operable tocommunicate with the tracking device 10 via a communication linkestablished between the short-range wireless data transceiver 48 and theshort-range wireless data transceiver 44. However the cargo sensor andtracking device may also be integrated into one unit, such as in FIG. 2.In this case, the cargo sensor 14 would look through the window todetect the presence or absence of a cargo container rather thandetermining if the tracking device 12 is connected to a trailer as inprevious embodiments.

Generally, the bottoms of cargo containers are corrugated, and as aresult, the distance between the bottom of the container and the surfaceof the trailer may range from almost zero to about 65 mm. Prior sensingtechnologies have been limited to a sense distance of around 15 mm, andas a result do not function reliably to sense a cargo container on aflatbed trailer. Using the technologies described herein, such as Timeof Flight, RF detection, or capacitive detection, the container sensingdevice 42 can detect the presence of a container on a trailer. RFdetection and capacitive detection have additional advantages in thatdirt or scratches on the sensor housing will not impact their ability todetect the container.

The power consumption of the container sensing device 42 is typicallyvery low. As a result, the device 42 can be powered solely by a primarycell that lasts for many years. This is particularly advantageous as thedevice 42 can communicate with the tracking device 10 via Bluetooth orother low-power wireless technology. The housing 50 of the device 42 canbe completely sealed, thereby reducing the cost of construction. Thehousing 50 can also be easily and quickly mounted on the trailer, asthere is no need to run a wire from the device 42 to the tracking device10.

FIGS. 6 and 7 depict a second embodiment for detecting and reportingwhether a cargo container is present on a flatbed trailer. Using thissecond embodiment, the operator of the fleet of trailers can determineremotely when a container is separated from or dropped onto the trailerbased on a measurement of the deflection of the suspension of thetrailer chassis when the container is mounted or dismounted. Thedistance of movement of the suspension is relative to the weight of thecontainer. This embodiment includes an inductive sensing device 42mounted on the underside of a chassis beam of the flatbed trailer inproximity to a suspension spring. The inductive sensing device 42includes a housing 62 in which an inductive sensing coil 54, aninductive sensing microprocessor 56, a short-range wireless datatransceiver 58, and a primary cell battery 60 are disposed. Theshort-range wireless data transceiver 58 may be a Bluetooth module. Thebattery 60 is configured to last ten years or longer.

In one preferred embodiment, the form factor of the housing 62 of thedevice 42 is three inches wide by 18 inches long by two inches high. Thedevice is preferably mounted underneath the main chassis beam that runsthe length of the trailer. The device 42 is attached to the chassis beamin a location that places the device 42 directly over one or more of thesuspension springs. The distance from the device 42 to the springs ispreferably between six and nine inches.

The device 42 continually monitors the relative proximity between thedevice 42 and the suspension spring. As a container is placed on thechassis, the suspension spring moves closer to the inductive sensingcoil 54 of the device 42 and this distance change is indicated by achange in voltage on the coil 54. The device 42 is designed with enoughsensitivity to detect small displacements in the suspension andtherefore be able to determine with relative accuracy the weight of thecontainer based on the displacement in the suspension spring.

In the preferred embodiment, the area of the inductive coil 54determines the distance at which movement is detected. Various models ofthe device 42 may have coils 54 if various sizes, such that a model maybe selected that has a coil size that maximizes the resolution in thedistance of the sensing for a particular chassis and suspensionconfiguration.

The foregoing description of preferred embodiments for this inventionhave been presented for purposes of illustration and description. Theyare not intended to be exhaustive or to limit the invention to theprecise form disclosed. Obvious modifications or variations are possiblein light of the above teachings. The embodiments are chosen anddescribed in an effort to provide the best illustrations of theprinciples of the invention and its practical application, and tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention as determined by the appendedclaims when interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

What is claimed is:
 1. A cargo tracking apparatus for detecting proximity to a cargo structure, the cargo tracking apparatus comprising: a housing having a sensor window, the housing configured to be attached to the cargo structure; a cargo sensor disposed within the housing and adjacent the sensor window, the cargo sensor for detecting a portion of the cargo structure disposed adjacent the sensor window and for generating a cargo sensor signal based on detection or lack of detection of the portion of the cargo structure; a location sensor disposed within the housing for generating location information based on a location of the cargo tracking apparatus; a processor disposed within the housing for receiving the cargo sensor signal and the location information, and based thereon generating alert messages containing the location information and information indicative of whether the cargo structure is disposed in proximity to the cargo tracking apparatus; and a wireless transmitter disposed within the housing for transmitting the alert messages.
 2. The cargo tracking apparatus of claim 1 wherein the cargo sensor comprises one or more of a Time of Flight (TOF) sensor, an optical sensor, a reed switch, a Radio Frequency (RF) sensor, and a capacitive sensor.
 3. The cargo tracking apparatus of claim 2 wherein: the sensor window in the housing is transparent at infrared wavelengths; the cargo sensor is a Time of Flight sensor that periodically makes a distance measurement through the sensor window, wherein the cargo sensor signal includes information indicative of the distance measurement; and the processor generates an alert message if the distance measurement is greater than a predetermined amount, thereby indicating that the cargo tracking apparatus is not in proximity to the cargo structure.
 4. The cargo tracking apparatus of claim 2 wherein: the sensor window in the housing is transparent at optical wavelengths; the cargo sensor is an optical sensor that detects the presence of the portion of the cargo structure adjacent the sensor window; and the processor generates an alert message if no portion of the cargo structure is detected adjacent the sensor window, thereby indicating that the cargo tracking apparatus is not in proximity to the cargo structure.
 5. The cargo tracking apparatus of claim 2, wherein the cargo structure includes a metallic portion, and wherein: the sensor window in the housing is transparent to Radio Frequency (RF) signals; the cargo sensor is a Radio Frequency (RF) sensor that is operable to detect presence of the metallic portion adjacent the sensor window; and the processor generates an alert message if the metallic portion is not detected, thereby indicating that the cargo tracking apparatus is not in proximity to the cargo structure.
 6. The cargo tracking apparatus of claim 2, wherein the cargo structure includes a metallic portion, and wherein: the sensor window in the housing is transparent to electric fields; the cargo sensor is a capacitive sensor that is operable to detect the presence of the metallic portion of the cargo structure adjacent the sensor window; and the processor generates an alert message if the metallic portion is not detected, thereby indicating that the cargo tracking apparatus is not in proximity to the cargo structure.
 7. An apparatus for detecting whether a cargo tracking device is attached to a cargo structure, the apparatus comprising: one or more first short-range radio frequency transceivers attached to the cargo structure; and the cargo tracking device configured to be attached to the cargo structure, the cargo tracking device comprising: a location sensor for generating location information based on a location of the cargo tracking device; a second short-range radio frequency transceiver for communicating with the one or more first short-range radio frequency transceivers via one or more communication links when the second short-range radio frequency transceiver is within communication range of the one or more first short-range radio frequency transceivers, wherein the second short-range radio frequency transceiver generates communication link status information indicating status of the one or more communication links; and a processor for receiving the location information and the communication link status information, and based thereon generating an alert message containing the location information and information indicative of whether the cargo structure is disposed in proximity to the cargo tracking device; and a wireless transmitter for transmitting the alert message.
 8. The apparatus of claim 7 wherein the one or more first short-range radio frequency transceivers are components of one or more sensor devices attached to the cargo container for monitoring one or more physical characteristics of the cargo structure.
 9. The apparatus of claim 7 wherein at least one of the one or more first short-range radio frequency transceivers is a component of a proximity button attached to the cargo structure.
 10. The apparatus of claim 7 wherein the processor generates the alert message only when the communication link status information indicates that all of the one or more communication links have been interrupted.
 11. The apparatus of claim 7 wherein the first and second short-range radio frequency transceivers comprise Bluetooth transceivers.
 12. The apparatus of claim 7 wherein the wireless transceiver comprises a cellular data transceiver or a Wi-Fi transceiver.
 13. An apparatus for detecting proximity of a cargo container to a trailer, the apparatus comprising: a container sensing device comprising: a first housing having a sensor window, the first housing configured to be attached to the trailer; a cargo sensor disposed within the first housing and adjacent the sensor window, the cargo sensor for detecting a portion of the cargo container that is adjacent the sensor window and for generating cargo sensor information based on detection or lack of detection of the portion of the cargo container; and a first short-range radio frequency transceiver disposed within the first housing, the first short-range radio frequency transceiver for transmitting the cargo sensor information via a wireless communication network; and a cargo tracking device comprising: a second housing; a second short-range radio frequency transceiver disposed within the second housing, the second short-range radio frequency transceiver for receiving the cargo sensor information via the wireless communication network; a processor disposed within the second housing for receiving the cargo sensor information and based thereon generating an alert message containing information indicative of whether the cargo container is disposed in proximity to the trailer; and a wireless transmitter disposed within the second housing for transmitting the alert message.
 14. The apparatus of claim 13 wherein the cargo tracking device includes a location sensor for generating location information based on a location of the cargo tracking device, and the processor generates the alert message including the location information.
 15. The apparatus of claim 13 wherein the cargo sensor comprises one or more of a Time of Flight (ToF) sensor, an optical sensor, a Radio Frequency (RF) sensor, and a capacitive sensor.
 16. The apparatus of claim 13 wherein the first and second short-range radio frequency transceivers comprise Bluetooth transceivers.
 17. The apparatus of claim 13 wherein the wireless transceiver comprises a cellular data transceiver or a Wi-Fi transceiver.
 18. A cargo detection apparatus for detecting the presence or absence of a cargo container on a cargo trailer having a chassis and one or more suspension springs, the cargo detection apparatus comprising: a housing configured to be attached to the chassis of the cargo trailer in proximity to at least one of the one or more suspension springs; an inductive coil disposed within the housing, the inductive coil for generating an inductive coil voltage having a level that is related to a distance between the inductive coil and the at least one suspension spring; a processor disposed within the housing, the processor executing instructions that determine a relative change in distance between the inductive coil and the at least one suspension spring based at least in part on a change in the inductive coil voltage; and a wireless transmitter disposed within the housing for transmitting information indicative of the state of the cargo container on the cargo trailer.
 19. The cargo detection apparatus of claim 18 wherein the information indicates the weight of the cargo container.
 20. The cargo detection apparatus of claim 18 wherein the information indicates if the cargo container is present or absent from the cargo trailer. 